N-(2-(6-fluoro-1H-indol-3-yl)-ethyl)-3-(2,2,3,3-tetrafluoropropoxy)-benzylamine is a potent and selective 5-HT6 receptor antagonist which is currently in clinical development. Its chemical structure is depicted below as Compound (I):

The synthesis of N-(2-(6-fluoro-1H-indol-3-yl)-ethyl-(2,2,3,3-tetrafluoropropoxy)-benzylamine, its use for the treatment of disorders such as cognitive dysfunction disorders, and pharmaceutical compositions comprising this substance are disclosed in U.S. Pat. No. 7,157,488 which further describes the preparation of the corresponding mono-hydrochloride salt.
An improved method for the manufacture of Compound (I) or salt thereof is disclosed in international patent application WO2011/076212.
Further, WO2016/091997 discloses the synthesis of N-(2-(6-fluoro-1H-indol-3-yl)-ethyl)-3-(2,2,3,3-tetrafluoropropoxy)-benzylamine by use of a supported Ni-catalyst with the use of sodiumborohydride as a reducing agent.
The final steps in the preparation of Compound (I) or pharmaceutically acceptable salts thereof as disclosed in WO2011/076212 are outlined in Scheme A:

The synthesis of Compound (IV) can conveniently be carried out as outlined below:

The synthesis of Compound (IV) comprises the following steps:                1) Subjecting 2,2,3,3-tetrafluoro-1-propanol to tosylation to yield Compound (VIII);        2) and reacting Compound (VIII) in a displacement reaction with 3-hydroxybenzaldehyde in the presence of a base to yield Compound (IV).        
The steps in the synthesis of Compound (I) as described above in scheme A consist of:                1) Hydrogenation of Compound (II) in the presence of a catalyst to obtain Compound (III), and isolation as L-(+)-tartaric acid salt (1:1) thereof (Step 1, Scheme A)        2) liberating Compound (III) from the L-(+)-tartaric acid salt (1:1) thereof (Step 2, Scheme A) to form the free base of Compound (III)        3) reacting the free base of Compound (III) with Compound (IV) in the presence of a reductant, specifically sodium borohydride to form Compound (I) (Step 3, Scheme A)        4) forming the HCl-salt (1:1) of Compound (I) (Step 4, Scheme A).        
However, the reduction with sodium borohydride in step 3 suffers from a number of drawbacks:                a) Long quenching times        b) Large amounts of waste are generated        c) Many unit operations (e.g. layer washings)        d) The formation of alcohol Compound (IX) also occurs in step 3 due to reduction of Compound (IV) with sodium borohydride, which leads to lowering of the yield of Compound (I):        
                e) The formation of stable boron-amine complexes, such as Compound (X), which are not easily converted into Compound (I) or removed:        
                f) The formation of enol ether Compound (XI) (E- and/or Z-isomer) which resides as an impurity in Compound (I) and salts thereof:        

Therefore, a more clean and productive process for the formation of Compound (I) is desirable. Such a process has been developed, and is disclosed in this patent application.